You just may want to join a ranger-led hike in Southwest Colorado's Mesa Verde National Park. You'll see a spot where the scrubby pinyon-juniper forest drops off. It falls into a sandstone chasm. It reveals a maze of 800-year-old stone dwellings. They are wedged beneath an overhang in the canyon wall. They're well preserved. It's easy to imagine you've stepped back in time. And that nothing has changed in this high desert landscape since the Ancestral Puebloans built these chambers. They were created in the 12th century.

But there's a modern problem. It is plaguing Mesa Verde. And it also plagues dozens of other national parks. It's air pollution. Mesa Verde lies downwind of several coal-fired power plants. They release nitrogen, mercury and sulfur. They go into the air. Meanwhile, huge natural gas fields lurk to the south. These belch methane. And as nearby towns and cities grow, everyday activities like driving increase levels of harmful ozone. Hundreds of years ago, Ancestral Puebloans would have been able to look out from Mesa Verde. They could see views that stretched 170 miles. Today, haze reduces those views. You can see just 66 miles on the worst days.

"Air pollution knows no boundaries," says Ulla Reeves. She is Clean Air Campaign Manager with the National Parks Conservation Association. It is a nonprofit that advocates on behalf of parks. She says pollution "reaches many, many miles away from the source." In Mesa Verde, one of the sources of pollution is Las Vegas. That city is 500 miles away.

An analysis was done last year. The NPCA found that even parks with the most protection under the Clear Air Act continue to experience pollution. The parks include some of the country's icons. Among them are Mesa Verde, Everglades, Yosemite, Acadia and Sequoia. The pollution can affect wildlife and human health, as well as the climate. According to the National Park Service's data, ozone levels on the peaks of the Great Smoky Mountains, for example, are nearly twice those in nearby cities. Atlanta is one. Up to 90 percent of black cherry trees in the park (depending on location) have sickly yellow leaves. They show ozone damage. And, they have other signs of ozone damage. Visitors with asthma can have trouble breathing. In California, Sequoia and Kings Canyon national parks regularly have ozone pollution that exceeds 70 parts per billion. That number is the standard set by the Environmental Protection Agency.

But air pollution doesn't stop at park borders. In 1999, the EPA created a regulation. It is called the Regional Haze Rule. It is designed to return visibility in 156 national parks and wilderness areas back to "natural" conditions. The plan is to cut emissions from polluters. These include coal-fired power plants. The rule only tackles visibility. But "the pollutants that affect visibility can also affect ecosystems and human health," says John Vimont. He is chief of the research and monitoring branch of the National Park Service's Air Resources Division.

The rule has played an important role. It has gotten some facilities to adopt cleaner technologies. Over the last 10 years, average visibility in Great Smoky Mountains National Park has risen. It has gone from 20 miles to 46 miles. This is according to Reeves. But there's still a long way to go. Visibility in the Great Smoky Mountains should be 112 miles on the best days. Part of the reason for the slow progress is because the rule is largely interpreted and carried out at the state level. This is instead of by federal agencies. Many states have struggled to muster resources and meet deadlines.

That's why the EPA is currently working on a series of changes. They are meant to strengthen the Regional Haze Rule. The changes will force states to keep more robust data on their progress. The states must submit regular plans. These are to ensure states meet legal requirements. And, they must cut emissions. At the same time, the changes allow states more time to implement their next round of plans.

Even if the Regional Haze Rule is strengthened, though, it'll still take a long time for the air in national parks to return to pre-industrial quality. The NPCA estimates that the soonest that goal could be achieved is 2064. Thirty out of 157 national parks are predicted to return to natural conditions by that year. Others, like Arizona's Saguaro National Park, might take much longer. It could be 750 years. Again, these dates don't take into account the latest changes. Those could speed up recovery time. But they're still a sobering reminder. On some of the most protected landscapes on the planet, the effects of human activity can linger well beyond our own lifetimes.

In Mesa Verde, natural resource manager George San Miguel is keenly aware of the effect that air pollution has on the park's visitors. Airborne nitrogen and sulfur are deposited into the soil. This leads to more invasive weeds. And fewer native grasses. Methane hovering overhead accelerates climate change. And then, of course, there are the views.

"One of the things we try to instill in visitors is a sense of going back in time," San Miguel says. "We want visitors to immerse themselves in the past. To put themselves in the sandals of the Native Americans that lived here, so to speak." To do that, he explains, you need to be able to see a long distance. This is because the Ancestral Puebloans likely used distant desert towers as navigation aids. Until Mesa Verde's natural visibility is restored, visitors remain solidly planted in the 21st century.

It is difficult to stop air pollution because it can go all over the place. Another way it is hard to stop air pollution is it makes yellow silky leaves. Fewer native grasses. And airborne nitrogen and sulfer are deposited into the soil.

joonhee0415-byo

6/28/2016 - 05:08 p.m.

It is difficult to stop air pollution at national parks because it goes away very fast and it is a type of invisible gas. Another reason why it is so difficult is because when you try to swipe it away it might still be there and the only thing that might do is go away in the air more higher so don't try that. I will tell my dad to stop smoking so it will cause less air pollution. This was an interesting article on tween tribune.